This disclosure is directed to systems and methods for detecting variations in composite structures using radio frequency (RF) transmission.
Composite materials, as discussed in this disclosure, refer to a class of materials that are prepared by combining two or more materials having different physical properties. Specifically, composite materials are those in which the different materials are combined in a manner such that they work together to optimize certain properties. These properties include, but are not limited to, lighter weights, increased strength and improved corrosion resistance. Such composite materials generally consist of a matrix or binder that surrounds, and bonds together, clusters of fibers that may be, for example, laminated in layers. In a layered configuration, each layer may have fibers arranged within the layer such that a principal direction of the fiber matrix is orthogonal to an arrangement of the fibers in an adjacent layer. Such an arrangement in the finished composite material yields increased strength and added fracture resistance in two orthogonally planar directions.
Composite materials, as discussed above, are generally those obtained by joining two or more materials, or two or more layers, by physical or chemical bonding methods. Composite materials may be formed in solid, laminated or laminated core constructions. The capacity of composite materials to exhibit improved strength to weight ratio characteristics make the use of these materials desirable in a number of applications where increased strength, resilience and flexibility of construction are desired. General fields in which the use of composite materials have gained wide acceptance include sporting goods, watercraft, automobiles, aircraft and spacecraft. Composite materials are, however, also applicable in other structures such as, for example, water towers and any manner of containers.
Composite materials, therefore, exhibit several advantageous characteristics. In the face of these advantages, a problem has been noted with composite materials, related to safety and/or consistency in manufacturing, with regard to structures manufactured from these materials. The difficulty is that, although structurally stronger than many of the materials from which like structures may have been traditionally manufactured, composite materials exhibit generally very limited elastic deformation. Though highly resistant to failure, when failure occurs, it is generally catastrophic. Such a disadvantage is particularly acute in the area of aircraft and spacecraft, where the use of composites has become more widespread, and where catastrophic structural failure may have most dire consequences.
The above difficulties are exacerbated by the fact that defects, changes, and/or damage to composite structures or composite components within structures are characteristically more difficult to detect with most conventional means.
Inspection of composite materials, composite material structures and/or composite material components is complicated, in a first instance, due to a general lack of any appreciable visible indicator of stress, deformation or other like indicator typically relied upon in structures manufactured from other materials to indicate potential for impending failure. Based on the generally layered and/or laminated nature of composite materials for use in structures and/or components, any “evidence” of impending failure may only lie in, for example, internal micro-fractures that may exist below the visible surface of the structure or component surface. As such, composite material failure is further particularly dangerous because composite material structures may often fail to exhibit any visibly-detectible signs of fatigue before complete failure.
As composite materials find utility in significantly broader applications, and the sheer number of structures manufactured from composite materials grows, and where, in particular, composite materials are employed in structures in which non-predictable and non-detectible catastrophic material failure may occur, the above-identified shortfall, and the effects thereof, become particularly more acute. For example, as the size of the fleet of new aircraft with composite material structures and components grows, and moreover, where a vast number of those components and structures age with use and wear, an ability to inspect the composite structures and components, particularly those used in aircraft, in a reliable manner, grows.